Process for making tacky acrylate microparticles and use therefor

Abstract

The present invention pertains to a process for preparing clusters of infusible, inherently tacky, elastomeric, solvent-insoluble, solvent-dispersible polymeric microparticles by aqueous emulsion polymerization. The invention also pertains to an adhesive comprising the polymeric microparticles and to a repeatedly reusable pressure sensitive sheet material having the elastomeric microparticles coated thereon.

We claim: 
     
       1. A process for preparing clusters of infusible, solvent-insoluble, solvent-dispersible, inherently tacky, elastomeric microparticles, comprising reacting a water-soluble redox initiator with an aqueous suspension comprising at least one stabilizer, at least one crosslinking agent, at least one emulsifier in an amount sufficient to produce monomer droplets having a particle size capable, upon polymerization, of forming microparticles individually being of from about 5 to about 200 microns in diameter, and monomers having at least one substantially water-insoluble ester of alkyl acrylate or methacrylate, under agitating conditions to produce a dispersion of the monomers in suspension, whereby the dispersed monomers polymerize forming clusters of elastomeric microparticles. 
     
     
       2. The process of claim 1, wherein the ester is isodecyl acrylate, isooctyl acrylate, 2-ethyl hexyl acrylate, n-butyl acrylate or isodecyl methacrylate. 
     
     
       3. The process of claim 1, wherein the ester is present at from about 95 percent to about 100 percent by weight of the monomers. 
     
     
       4. The process of claim 1, wherein the oxidizing agent of the redox initiator is ammonium persulfate or sodium persulfate. 
     
     
       5. The process of claim 4, wherein the ammonium persulfate or sodium persulfate is present at from about 0.25 to about 1 percent by weight of the monomers. 
     
     
       6. The process of claim 4, wherein the redox initiator further comprises ethylenedinitrilotetraacetic acid sodium iron(+3) salt (EDTA-Fe(3+)) and a second reducing agent. 
     
     
       7. The process of claim 6, wherein the EDTA-Fe(3+) is present at about 0.05 percent by weight of the monomers. 
     
     
       8. The process of claim 6, wherein the second reducing agent is sodium formaldehyde sulfoxylate. 
     
     
       9. The process of claim 8, wherein sodium formaldehyde sulfoxylate is present at about 0.5 percent by weight of the monomers. 
     
     
       10. The process of claim 1, wherein the stabilizer is methyl cellulose, hydroxy propyl cellulose, hydroxy propyl methyl cellulose or ethyl cellulose. 
     
     
       11. The process of claim 10, wherein the stabilizer is present at up to about 2 percent by weight of the monomers. 
     
     
       12. The process of claim 1, wherein the emulsifier is sodium dodecyl benzene sulfonate, sodium salts of alkyl aryl ether sulfonate, alkyl aryl ether sulfonate or alkyl aryl polyether alcohol. 
     
     
       13. The process of claim 12, wherein the emulsifier is present from about 0.5 to about 1.5 percent by weight of the monomers. 
     
     
       14. The process of claim 1, further comprising removing the elastomeric microparticle clusters from suspension by filtration. 
     
     
       15. The process of claim 1, wherein the elastomeric microparticles comprise from about 95 percent to about 99 percent by weight isodecyl acrylate and from about 1 percent to about 5 percent methacrylic acid.